From there, the deep blue of the Pacific Ocean comes back into view, and if you squint, you can see downtown Los Angeles 30 miles off on the horizon.

Some days, you can also see wild bison.

"This is a really common place to see a bison, you'll see them in groups, and then solitary males, very frequently in this stretch of road," says John Mack, chief conservation officer for the private Catalina Island Conservancy, which manages most of the land here.

As if on cue, a couple minutes later, a lone male bison comes into view, standing stoically atop a ridge of a hill blanketed with scrub oak trees.

"It's, well, an interesting thing to see," biologist Julie King says from the back seat.

King is in charge of managing the 150 wild bison roaming the island. They're by no means native. Fourteen of the animals were brought here in 1924 by a Hollywood crew for a film shoot. The movie never got made, and the bison were never returned to the wild.

"Logistically, probably, it was too difficult, and I'm guessing they thought bison were a lot like cattle, that you could turn them loose and herd them fairly easily," King says.

You can't. They jump fences. Or plow right through them. And with no natural predators, their population exploded. At one point in the 1980s, there were more than 600 here. That's when the conservancy sprang into action. There was some hunting. But mostly the group paid to ship excess bison, by barge, over to the mainland and eventually to tribes in South Dakota.

But lately, King and her team have discovered a new, cheaper solution: contraception.

Each spring, the team sets out into Catalina's backcountry on foot, armed with dart guns and a birth control vaccine called porcine zona pellucida, or PZP.

"You have to be careful because they will charge," says King, who adds she's had that happen on more than one occasion after successfully hitting a female cow with the PZP-filled dart.

But she says the risk is worth it because the contraception program is yielding some impressive early results. Since it began three years ago, the conservancy has managed to bring the herd down to 150 animals; the number they consider sustainable.

No more shipping, no more hunting and no more culling.

That's starting to get people's attention in places where bison are a problem, like Yellowstone National Park.

"The problem is reproduction, you can remove animals till the cows come home and you haven't solved the problem," says Jay Kirkpatrick, director of the Science and Conservation Center at Zoo Montana.

Kirkpatrick says all eyes are on the work that's being done with bison on Catalina Island. He hopes the early successes will bolster support for a similar solution in Yellowstone. The herd there is also too big for the park, and right now bison that roam outside and onto land grazed by cattle are sometimes shot.

Kirkpatrick says the PZP vaccine has been successful on female bison in zoos for 20 years. The privately owned Catalina Island is the first place contraception is being used on bison in the wild.

Even though bison aren't supposed to be on Catalina Island, King says removing the animals altogether is off the table.

They're big business. Each summer, thousands of tourists climb into those Jeeps for a day trip into the interior.

"So many people come here because it's closer than going to South Dakota or to Montana to see bison," King says.

Copyright 2014 NPR. To see more, visit http://www.npr.org/.

Transcript

RENEE MONTAGNE, HOST:

And, David, let's go now to an island not far from our studio, here in Southern California. As the 1950s hit song put it: Twenty-six miles across the sea, Santa Catalina is waiting for me. It's a famously romantic destination and an unlikely place for a herd of wild bison - far from their native prairie. Over the years, Catalina's bison have paired off and reproduced so much, officials are tackling the problem of overpopulation, now, with birth control.

NPR's Kirk Siegler paid a visit.

KIRK SIEGLER, BYLINE: It's a bone jarring ride as our open-aired Jeep winds and climbs, twists and turns, for miles into Catalina Island's vast interior. Two thousand feet up and the deep blue of the Pacific comes back into view - if you squint, even downtown L.A. But we're not here for the views.

JOHN MACK: This is a really common place to see a bison, right? You'll see them in groups, and then solitary males, very frequently in this stretch of road.

SIEGLER: This is one of our guides, John Mack. He's chief conservation officer for the private Catalina Island Conservancy, which manages most of the land here.

Biologist Julie King chimes in from the backseat. And she's in charge of managing Catalina's bison herd.

KING: It is an interesting thing to see. And...

SIEGLER: Yeah, interesting, a wild animal from the Great Plains on an island off the coast of California. It's like we've stepped into a scene from a low-budget movie. Well, in some ways, we have. See, way back in 1924, a Hollywood crew brought 14 bison to this island for a film shoot. The movie? It never got made. The bison? They got left behind.

KING: Logistically, probably, it was too difficult, and I'm guessing they thought bison were a lot like cattle. That you could turn them loose and herd them fairly easily and keep them confined and do a spot.

SIEGLER: You can't. They jump fences or plow right through them. And with no natural predators, their population exploded. At one point there were more than 600 here. That's when the Conservancy sprang into action. There was some hunting. But mostly they paid to ship excess bison, by barge, over to the mainland, and eventually to tribes in South Dakota. So lately, Julie King and her team have discovered a new, cheaper solution - contraception.

KING: In order to load a dart...

SIEGLER: Bison birth control, in the form of a dart that King is loading into the chamber of a rifle.

KING: Because you're watching, I'll probably miss.

MACK: Yeah. The pressure is on.

SIEGLER: The dart holds a needle with a contraception vaccine called PZP.

(SOUNDBITE OF SHOT)

SIEGLER: Bull's eye.

MACK: Bull's eye.

KING: Bull's eye.

SIEGLER: Bull's eye. On a pillow propped up on a plastic chair 30 yards away, King is demonstrating what she actually does every spring, on foot, sometimes miles away from the safety of a jeep, by the way.

KING: You have to be careful, because they will charge.

SIEGLER: Have you ever had that happen?

KING: Yes.

(LAUGHTER)

SIEGLER: All in a day's work. But King says the risk is worth it. The contraception program is yielding some impressive early results. They've managed to bring the herd all the way down to 150 animals, the number they consider sustainable. No more shipping, no more hunting, no more culling. And that's getting people's attention in places where bison are a problem, like Yellowstone National Park.

JAY KIRKPATRICK: The problem is reproduction. You can remove animals 'till the cows come home and you haven't solved the problem.

SIEGLER: Jay Kirkpatrick runs the Science and Conservation Center at Zoo Montana. He hopes the successes on Catalina Island will bolster support for a similar solution in Yellowstone. The herd there is also too big for the park and right now, bison that roam outside it and onto land grazed by cattle are often shot.

KIRKPATRICK: There, I would institute a program where you just cruise around the park with a cooler full of vaccine and darts and your gun and you know what happens when they get out on the road, and they won't even get out of the way of vehicles. You could just sit in your vehicle and dart away.

SIEGLER: Kirkpatrick is being a little facetious of course. But he says the PZP vaccine has been successful on female bison in zoos for 20 years, and all eyes are now on Catalina Island. It's the only free-ranging bison herd in the U.S. that's being managed with contraception.

Biologist Julie King says removing bison all together is off the table. They're big business.

KING: So many people come here because it's closer than going to South Dakota or to Montana to see bison.

SIEGLER: Each summer, thousands of tourists climb into those jeeps for a day trip into the interior and a chance to catch a glimpse at a wild bison roaming a Pacific Island.